Heater oil purification using sulfur dioxide and a halogen



Dec. 13, 1955 H. s. sEELlG ErAL HEATER OIL PURIFICATION USING SULFUR DIOXIDE AND A HALOGEN Filed Nov. 26, 1952 ATTORNEY oil.

United States Patent O HEATER OIL PURIFICATION USING SULFUR DIOXIDE AD A HALGGEN Herman S. Seelig, Valparaiso, Carl E. Johnson, Grilith, and John F. Deters, Valparaiso, Ind., assignors to Standard Oil Company, Chicago, Ill., a corporation of Indiana Application November 26, 1952, Serial No. 322,756

13 Claims. (Cl. 196--24`) This invention relates to the relning of straight run petroleum distillates boiling in the heavier-than-gasoline range. More particularly it relates to the production of a sweet, good color, good copper strip and good burning quality heater oil by the treatment of a sour, high sulfur virgin petroleum distillate boiling between about 300 and 650 F A very large demand exists for petroleum distillates which boil in the heavier-than-gasoline range, i. e., within the range between about 300 and 650 F. These distillates have a tremendous demand for use in domestic heating installations; oils for this purpose are generally known as burning oils, furnace oils, or heater oils. Still another large demand for these distillates is for illumination purposes; oils for this use are generally called kerosene or burning oil. Another large use for oils of this type is as fuels for diesel engines. A rapidly growing use for oils of this type is in the reaction propulsion engine, i. e., jet propulsion; oils for this use are generally called jet fuels or IP-fuels. ln general straight run (virgin) distillates are preferred t'or these uses. Consumer demand has forced the industry to produce oils of this type which are low in mercaptan-odor, i. e., very low in mercaptan number or even sweet to the doctor test. AFurthermore, consumer demand has forced the industry to produce oils that are of relatively low aromatic hydrocarbon content. At this time the industry is making a greater effort to produce oils of relatively low total sulfur content, i. e., oils containing on the order of 0.25 weight percent sulfur.

In addition to the requirement for a sweet product of 'relatively low sulfur content, a demand has arisen for 'domestic heating oils of improved color and corrosiveness. in most instances a color of -l-ltl Saybolt is satisfactory. However, highest quality heater oil has a stable color of about -l-lS Saybolt.

oil has a Bolt copper strip number of 3 or less.

'Y The doctor process has been used successfully to sweeten these heavy distillates and is being used commercially in spite of the increase in sulfur content of the product The doctor process for this use has a disability in that the burning quality, as measured by deposits formed 'in domestic oil burners, is adversely alected.

For many years the burning quality of kerosenes has been improved by an extraction treatment with liquid SO2 in the Edeleaneu process. This treatment removes appreciable amounts of aromatic hydrocarbons and organic sulfur compounds from the raw distillate. The treatment of furnace oils and heater oils with liquid SO2 definitely improves the burning quality thereof, as measured by the deposits in domestic oil burners. However,

lthe SO2 treatment of a sour distillate does not produce a sweet product even though the mercaptan number is usually decreased by the SO2 treatment.

lt is an object of this invention to produce a substantially sweet oil of good color stability, good burning quality and Satisfactory corrosiveness to copper by the The corrosiveness of the Voil is measured by a copper strip method; a satisfactory ICC treatment of a virgin petroleum distillate boiling in the heavier-than-gasoline range. A particular object is to produce an oil suitable for use as domestic heating oil, burning oil and jet fuel by the treatment of a straight run petroleum distillate boiling in the range of about 300 to 650 F. Speciiically the object of the invention is the treatment of a virgin, sour, high sulfur heater oil in a combination process utilizing liquid sulfur dioxide, a sweetening agent and aqueous caustic to produce an oil which is substantially mercaptan-free, of good color stability, of good burning quality and of satisfactory copper strip number.

The above objects and other objects not set out in detail are attained as follows: A sour, virgin petroleum dis` tillate boiling in the heavier-than-gasolne range is contacted in the liquid phase in a rst zone with sucient liquid SO2 to form a rafnnate phase and a liquid SO2-rich extract phase, in the presence of an amount of a sweetening agent, hereinafter defined, sufficient to substantially sweeten said distillate. The sweetening agent is selected from the group consisting of chlorine, sulfuryl chloride and thionyl chloride. The contacting in the rst Zone is carried out at a temperature below about +70 F, for a time suflicient to substantially sweeten the distillate. The rafdnate phase from the rst zone is contacted in the liquid phase in a second zone at a temperature below about 70 F. with enough liquid SO2 to form a second rainate phase and an extract phase. The second rainate phase is processed to remove occluded and dissolved SO2 in order to recover a substantially sweet product oil therefrom. lt is preferred that the last traces of SO2 be removed from the nal rainate phase by treatment with aqueous caustic solution.

The process of this invention is particularly beneficial when applied to petroleum distillates which boil in the heavier-than-gasoline range and which are derived by distillation of crude oil. These distillates are commonly known as straight run or virgin distillates. ln general the heavier-than-gasoline boiling range distillates. boil within the range of about 300 to 650 F. Although the process can be applied to any mercaptan containing, i. e., sour, straight run petroleum distillate, it is most suitable to the rening of those distillates which are high in sulfur content, i. e., distillates which contain more than about 0.3 weight percent sulfur. A preferred feed stock to this process is a sour, high sulfur straight run petroleum distillate which boils within the range of about 350 to 625 F. High sulfur crudes such as West Texas crude and most California crudes provide distillates which are particularly suitable for treatment by this process.

It has been discovered that sour distillates can be sweetened by contacting them with an amount of liquid SO2 in excess of the solubility of SO2 in the liquid distillate under the conditions of contacting, in the presence of an effective amount of a sweetening agent. The sweetening agents of this invention are free-chlorine, C12; sulfuryl chloride, SO2C12; thionyl chloride, SOCI-2. While it is possible to obtain a sweet product oil in this manner, this product oil does not have a satisfactory color stability. It has been discovered that a sweet oil having good color stability and satisfactory corrosiveness can be prepared in a stepwise process by contacting the sour distillate with liquid SO2 suilicient in amount to form separate rainate and extract phases in the presence of about the minimum amount of sweetening agent needed to obtain substantial sweetness for a sufficiently short contacting time. ln the second step the railinate phase fromthe sweetening step is extracted with suflicient liquid SO2, in the absence of additional sweetening agent, to produce separate rafl'lnate and extract phases. The second raffinate phase may be extracted with liquid SO2 alone in a third step, if desired. The product oil derived by the reoil.

3 moval of occluded and dissolved SO2 from the second (or third) ratiinate phase is sweet, of good color stability, and of satisfactory corrosiveness to copper.

Further, the use of more than the minimumamounts of sweetening agent needed to obtain a sweet product oil results in a product oil that is excessively corrosive. has been discovered that this oversweetened oil can be made of satisfactory copper strip number by treating the second raffinate phase as such, or after removing occluded and dissolved SO2, with hot aqueous caustic solution, i. e., treating at a temperature between about 123 and 220 The sweetening agent of'this invention is selected from at least one member of the group consisting of chlorine, sulfuryl chloride and thionyl chloride. The presence of trace amounts will reduce the mercaptan content of the raffinate oil. In order to obtain a product oil that is sweet or substantially so, itis necessary to use about mol of chlorine or sulfuryl chloride per mol of mercaptan in the feed oil; or about 1.5 mols of thionyl chloride per mol of mercaptan in the feed oil. The exact amount of sweetening agent needed to attain a substantially sweet oil will vary somewhat depending on temperature, contacting time and Contactin" efficiency. ln general a substantially sweet oil can be obtained with the following quantities of sweetening agent: chlorine or sulfuryl chloride, between about 0.9 and 1.1 mols per mol of mercaptan; thionyl chloride, between about 1.4 and 1.6 mols per mol of mercaptan. Y

The presence of amounts of swcetening agent in excess of the amounts given above has an adverse effect on the color stability, the copper strip number and the burning quality of the product oil, i. e., if Yno special treatment is given to overcome this adverse effect. However, it may be desirable to use a slight excess of sweetening agent and overcome the adverse effects by hot caustic treatment. ln general there is no advantage to using more than about 1.3 mols of chlorine or sulfuryl chloride. More than this amount of sweetening agent results in increased chlorination of the product oil without beneficial effect.

The time of contacting of the feed oil, liquid SO2 and sweetening agent must be sufficiently long to complete the sweetening reaction. However, prolonged contacting beyond the time needed for sweetening has an extremely adverse effect on the copper strip number of the product At the temperatures of operation the product oil will be substantially sweet with l or 2 minutes of efiicient contacting.Y The higher the temperature the less time needed. The lower the temperature the more contacting that can be carried out without adverse effect on copper strip number. in general it is preferred to contact for a time between about 2 minutes and l0 minutes. Y

The time of contacting of the raffinate phase containing the sweet oil and the liquid SO2 should belong enough to permit the liquid SO2 to extract the bodies which have an adverse effect on color stability. Prolonged contacting has no adverse effect on the properties of the oil from the liquid SO2 extraction step. Thus contacting times may be between about 2 minutes and 60 minutes.

The temperature of contacting of the feed oil and the liquid SO2 in the presence of sweetening agent in the first step and with liquid SO2 alone in the second step, or subsequent treatment with liquid SO2 alone, should be below about +70 F. in order to obtain a product oil of good burning quality. Lower temperatures are desirable and temperatures as low as 70 F. may be used. Best results .on burning quality and other characteristics of the product oil are obtained by operating at a temperature between about +30 and 40 F. Different temperatures may be used in the sweetening step and in the subsequent liquid SOz extraction step(s).

When operating with feed oils of very high viscosity and/or comparatively high solid points, the feed oil may be diluted with a low freezing point, low viscosity oil which can be readily separated from the product oil by 4 distillation. Examples of suitable diluent oils are Vbutan pentane, hexane.

The contacting in the sweetening step and liquid SO2 extraction step may be carried out batchwise in one or more separate stages; for example, in a batchwise operation, part of the sweetening agent may be introduced in a first stage along with liquid SC2 and the remainder ofv thc sweeteuingragent introduced in a second stage along with liquid SO2. A separation of a raffinate phase from an extract phase may be made between each of thesweeteniug stages and the raffinate phase alone sent to the second sweetening stage; or the total material from the first stage may be sent to the second stage, in which case additional liquid SO2 may or may not be added. The liquid S02 extraction of the sweet raffinate phase from the sweetening step may be carried out in one, two or more separate Y steps, preferably with a separation of raffinate phase from extract phase between each step.

It is preferred to carry out the sweetening and liquid SO2 extraction steps in a continuous countercurrent extraction tower. By the use of atower the Vliquid SC2 usage is mininii'fed for a product oil of good quality. ln a countercurrent tower the total liquid S132 may be introduced at an upper point in the tower, e. g., near the top thereof; the feed oil may be introduced at a lower point in the tower, e. g., near the bottom thereof; and the sweetening agent may be introduced at an intermediate point, e. g., near the vertical mid-point of the tower; or the sweetening agent may be introduced at several points along the height of the tower. in any event, at least one theoretical extraction stage should be present in the tower for the contacting of the feed oil with liquid SO2 and sweetening agent. At least one theoretical extraction stage should be available for the contacting of the substantially sweet rafiinate phase with liquid SO2, in the absence of additional sweetening agent.

In the sweetening step and the liquid SO2 extraction step, the liquid SO2 must be present in an amount at least sufiicient to produce separate rainate and extract phases. This minimum amount will vary with the temperature of contacting. In general 20 volume percent of liquid SO2, based on charge to the contacting, will produce distinct raffinate and extract phases at the preferred temperatures of operation. More than this minimum amount is preferred, and amounts as much as 500 volume percent, may be utilized. It has been found that very little improvement in burning quality is obtainable by using very large amounts of liquid SO2 even thoughthe yield of product oil is markedly decreased. It is preferred to yoperate with the liquid SO2 usage between about 20 and volume percent, based on charge.

When the process of this invention is being carried out in batchstages, suicient liquid SO2 must be added in each stage to produce separate raffinate and extract phases, and preferably the usage should be between about 20 and 80 volume percent, based on charge tothe parv ticular stage. When the process is being carried out in Va countercurrent tower, the vliquid SO2 usage should be at least enough to produce distinct rainate and extract phases. It is preferred to operate with between about 20 and 80 volume percent of liquid SO2, based on feed oil charged to the tower.

When the sweetening agent usage is limited to approximately that amount needed to sweeten the feed oil, it has been found that the method of removing occluded and dissolved SO2 from the final raflinate phase to produce a neutral product oil is of little moment in regard to the properties of the product oil, i. e., the dissolved and occluded SO2 can be completely removed by stripping with an inert gas such as propane or nitrogen; or

the SO2 may be weathered away by heating to a moderate temperature for a period of time, or the SO2 may be removed by treatment with aqueous NaOH or KOH solution; or preferably a combination of stripping and aqueous caustic treating. In the case of the SOzClz 'ajraaesg Vsweetening agent, the maximum usage without harmful eifect is about 1.1 mols per mol of mercaptan.

When the sweetening agent usage has been limited to approximately the amount needed to sweeten the feed oil, the concentration of the aqueous caustic solution and the temperature of aqueous caustic treatment has no appreciable eiect on the properties of the product oil. The aqueouscaustic solution may contain from about 5 to as much as 50 weight percent of sodium hydroxide or potassium hydroxide. The temperature of aqueous caustic treatment may vary from ambient temperature to about 220 P.

It has been mentioned previously that the use of amounts of sweetening agent in excess of about 1.1 mols in the case of chlorine or sulfuryl chloride has an adverse eiect on the copper strip number and color stability of the product oil. It has been found that these adverse eiects can be overcome by treating the final raliinate phase or nal SO2-free rainate with a concentrated aqueous caustic solution at elevated temperature. By treating at about ambient temperature with aqueous caustic solution containing about weight percent or more caustic, it is possible to obtain a satisfactory copper strip number. At this aqueous caustic concentration it is possible to improve copper strip number and also the color stability by treating at elevated temperatures, preferably at least about 120 F. In some cases it may be desirable to operate at temperatures on the order of 220 F.

At least enough aqueous caustic solution should be used to obtain a neutral product oil. The amount of aqueous caustic used may be from between about l0 and 100 volume percent, based on oil.

The caustic treated oil normally will contain some occluded caustic solution. This occluded solution may be removed by water washing or by passing the oil through a bed of crushed rock salt.

The annexed drawing which forms a part of this specilication shows in schematic form one embodiment of the process of this invention. It is to be understood that many items of process equipment have been omitted and that these may readily be added by those skilled in the art.

In the drawing sour distillate feed from source 11 is passed through line 12 into a deaeration unit 13. The feed stock in this illustration is a virgin heater oil derived from the distillation of West Texas crude, which oil has a mercaptan number of 70 and a sulfur content of about 0.7%, a phenol content of 0.2%, and an A. S. T. M. boiling range between about 330 and 550 F.

Deaeration unit 13 may comprise conventional equipment such as the vacuum deaeration equipment ordinarily employed in commercial processes of liquid SO2 refining of hydrocarbon oils. The deaerated feed is passed from deaerator 13 through line 14 into drying zone 16. Water is harmful to the extraction process and it is preferred that the feed oil be substantially dehydrated. Drying zone 16 may comprise conventional equipment and drying reagents, e. g., drier 16 may be a vessel packed with calcium chloride, rock salt, magnesium silicate, alumina gel, etc. In some instances it may be desirable to dehydrate by means of vacuum distillation. It is to be understood that the specific form of deaerator 13 and drier 16 is no part of the present invention and that any treatment may be used which substantially eliminates air and water from the feed.

The oil from drier 16 is passed through line 17 and through heat exchanger 18 where the temperature of the oil is lowered to the desired operating temperature, herein 10 F. The cold oil is passed through line 19 into a lower portion of extractor 21. Y

Extractor 21 is a tower packed with suitable materials in order to increase the efiiciency of contacting of the feed and the liquid SO2. For example,rextractor 21 may be packed with Berl saddles, glass, or metal spheres, alumina balls, jack chain, etc. Also, extractor 21 may be provided with reboiler 36.

in the form of a bubble tower which has been arranged for extraction purposes. Extractor 21 may also be pro; vided with mechanical agitators arranged along the height of the column to improve agitation.

Extractor 21 may also be provided with heat exchangers to permit control of the temperature of contacting or to permit operation with a temperature gradient within the tower.

Liquid SO2 from source 22 is passed through valved line 23 into an upper portion of extractor 21. The ex traction must be carried out under liquid conditions and surhcient pressure must be applied to extractor 21 in order to maintain the SO2 in the liquid phase. In this illustration the total amount of liquid SO2 used is 75 volumes per volumes of feed oil. At least one theoretical extraction stage is present in the upper zone of extractor 21 and the contacting time therein is about 3 minutes. n

Although chlorine gas reacts with SO2 to form sulfuryl chloride, it has been found that the chlorine content of the product oil when using chlorine as the sweetening agent is higher than when using sulfuryl chloride as the sweetening agent. It is preferred to use sulfuryl chloride as the sweetening agent. In this embodiment 1.2 mols of sulfuryl chloride are used per mol of mercaptan in the feed. The sulfuryl chloride from source 24 is passed through line 25 into extractor 21 at about the vertical midpoint of extractor 21. If preferred the sulfuryl chloride could be introduced at various points along the height of the tower. Of course it is necessary to provide at least one theoretical extraction stage above the last point of sulfuryl chloride introduction and the exit of the extractor. Here# in a moderate excess of sulfuryl chloride is used in order to insure sweetening with the relatively short contact time of 3 to 4 minutes in .the lower sweetening zone ofthe extractor. It is preferred to maintain the interface somei what above the point of entry of the sulfuryl chloride, but below the point of entry of the liquid sulfur dioxide.

From the bottom of extractor 21 an extract phase is removed and is passed through line 26 into stripper 27 which is equipped with a reboiler 28. In .stripper 27 the SO2 is removed from the extract and is taken overhead through line 29. 'A substantially SO2-free extract is removed rom stripper 27 through line 31 and is sent to storage not shown.

The raiiinate phase is removed from extractor 21 through line 33 and is passed into stripper' 34 which is In stripper 34 most of the occluded and dissolved SO2 is removed overhead by Way of line 37 and is passed into line 29.

In the course of operation some impurities such as Water and H28 pass into the SO2 and these should be removed before the SO2 is recycled to the process. The contaminated SO2 in line 29 is passed into purication zone 38 where the impurities are removed. The purified SO2 is passed through line 39 into line 23 and is reused in extractor 21. Puriiication zone 3S is shown schematically and may be any conventional equipment such as is used in liquid SO2 relining of hydrocarbon oils.

The substantially SOZ-reeranate oil is removedtirom stripper 34 by way of line 4I wherein it meets a stream of aqueous caustic'rsolution.Y Aqueous caustic solution containing 30 weight percent NaOH is passed from source 42 through line 43, heat exchanger 44 and line 45 into line 41. The aqueous caustic solution is raised to a temperature of about 175 heat exchanger 44. The mixture in line 41 is passed into mixer 46 wherein the oil and aqueous caustic are thoroughly intermingled in order to neutralize the SO2 remaining in the oil and remove bodies deleterious to copper strip number and color stability. Mixer 46 is provided with a heating coil 47 which maintains the contents of the mixer at a temperature of about F. YIn this embodiment about 35 volume percent of aqueous caustic solution is used per volume of oil in line 41.

The mixture of oil and aqueous caustic is passed through line 49 into settler 51 where two phases separate. The lower aqueousV caustic phase is removed from settler 51 by way of line 52 and isV sent to spent caustic disposal. The aqueous causticvmay be recycled by way of valved vline 53 to line45 for reuse in the treating. The neutralized Voil is withdrawn from settlerV 51 by way of line 56.

Water from source 57 is introduced by way of line 58 into line V56 where it-meets the oil from settler 51. The oill and water are passed into mixer 59V where the two are thoroughly intermingled, in order to permit the water to extract-.tracesof aqueous caustic solutions from the oil. The mixtureVA is passed by way of line 671 into settler 62 where two phasesY separate. The lower water phase is withdrawn by way of line 63 and is sent to disposal. The finished product oil is withdrawn by way of line 64 and is sent to storage not shown. Y

Instead of using water wash to remove occluded aqueous caustic solutiona salt drum may be utilized. A salt drum consists ofra vertical vessel containing a bed of coarse rock salt. The coarse rock salt removes the occluded aqueous caustic solution which is withdrawn from the salt Y drum in the form of a brine. The product oil is withdrawn from the top of the salt drum.

The results obtainable by the process of this invention are illustrated below. In these experiments the raw oil was contacted` with liquid SO2V and sweetening agent or liquid SO2 alonein a glass reaction vessel provided with a 10,000 R. I. M. stiffer. The raw oil Awas introduced into the vessel and the liquid SO2 was added and the contents brought tothe desired temperature. .Then the desired amount of sweetening agent was added to the reaction vessel and the contacting continued for the desired length of time. After the desired period of contacting the contents were settled and the separate raffinate and extract phases withdrawn. d Y

The Vrainate phase from the sweeteuing step was then contacted with liquid SO2 in the reaction vessel at the desired temperature for the desired time. The separate phases from.V this second contacting step were withdrawn and the second ratlinate phase, usually,V was given another Y contacting with liquid SO2. t Y

A three-stage batch contacting as described above is about the equivalent of a countercurrent contactingusing about one-half the liquid SO2 used inrthebatch contacting. t The raw oils used in these experiments were derived by distillation Afrom a West Texas crude. Each of the feed oils lies inthe so-called heater oil classification. The physical characteristics of the feed oils are given below:

HEATER OIL FEED AGED COLOR Extensive investigation has indicated that the color stability on storage of a distillate in the heavier-than-gasoline boiling range can be predicted by means of a laboratory method. The results of this laboratory method are known as agedrcolorf In this test 100 ml, of oil are maintained in an open beaker exposed to atmospheric oxygen for hours at 200 F. At the end of the 20 hours the Saybolt color of the oil is determined. This color is the aged color of the oil; An aged color of 10 Saybolt indimeet the most stringent commercial specifications on color t stability in storage.

COPPER STRIPv NUMBER The corrosiveness of Van oil is ldetermined by its effect on the color of a copper strip. The copper strip corro-k sion is determined for heater oil by immersing a copper strip in the oil for 3 hours at 212 F.V The corrosiveness of the oil in this speciiication has been determined by the Bolt copper strip number technique. This technique is describedin the August 9, 1947, issue of thek Oil and Gas Journal. In this method the number 0- is assigned t0 a perfect,strip, i. e., equal to a strip prior to being used in a test. The higher the number assigned to a strip after the test, the more corrosive the oil. A satisfactory heater oil should have a copper strip number of 3 or less. d

STEEL DISH GUM It has been found that sleeve-type burners in domestic heating installations are most markedly affected by the tive sleeve-type burner.

standard test burner for determining the burning quality of domestic heating oils. Afull scale test using the Jungers burner involves the burning of many gallons of oil and many days of operation. AV simple laboratory procedure has been developedwhich adequately predicts the results obtainable in the full size Iungers burner test. This laboratory method is known as the steel dish de- Y posit test or steel dish gum'test. Y

The steel dish deposit test is carried out as follows: An

18-8 stainless steel dish is maintained at a temperature of 500 F. by means of a hot plate. .The dish is saucershaped and has the following dimensions: Outside diameter, 2 inches; thickness at the edge, ZV1@ inch; thickness at the center of the dish, 3/16 inch. The depression in the dish corresponds to a section of a sphere.Y The dish is provided with a thermocouple which permits the temperature of the dish to be measured. The dish is placed on a hot plate, the temperature of which is adjusted to maintain the dish at about 500 F. The oil to be tested is dripped at a substantially constant rate onto the dish. The rate of evaporation of the oilffrom the dish should be substantially equal to the rate f addition of the oil to the dish, i. e., the dish always contains a film of liquid oil. A 400 ml. sample of oil is used in each test and the oil 'is added dropwise to the dish at aV rate of about 1 ml. per minute. Atthe completion of the test the dish is removed from the hot plate and allowed to cool. The difference in the weight of the dish before and after the test is called the steel dish deposit.

A large number 'of tests on many different oils have been made and it has been found that an oil which gives a steel dish deposit of 10 mg.V will operate satisfactorily in a Iungers burner.

In all cases oils produced by the process of this inven- Vtion had a satisfactory steel dish gum test.

Test 1 In this test the Veffect of variation in the amount ofV 9 aqueous NaOH solution containing 10% NaOH at about 70 F. The results of this test are given below:

Product Oil Run Mols SOzClz M01 RsH Mercn Copper Aged Nujer Strip Color 0. 7 6. 4 o +30 1. o o 2 +30 1. 3 o 4 +29 7. 5 0 Black -16 Test 2 In this test the etect of Contact time was determined when operating on feed B under the same condtions as given in Test 1 above and when using 1.3 mols of sulfuryl chloride per mol of mercaptan in each run.

Product Oil Time, Minutes Metrcapan Copper Number Strip Aged Color Test 3 1n this test a series of runs was made on feed B under the conditions of Test l except that in each run 1.0 mol of sulfuryl chloride was used per mol of mercaptan; and the effect of temperature, at constant caustic concentration, was determined at two different caustic concentra- The above data show that when using the theoretical amount of sweetening agent the caustic concentration and the temperature of caustic treating have little appreciable effect on the copper strip number and aged color of the product oil. In all runs above the product oil was sweet Yto the doc tor test. p

Test 4 In this test runs were made on feed B under the conditions of Test 3 except that an excess of sweetening agent was used. In this test 1.3 mols of sulfuryl chloride were used per mol of mercaptan in the feed. The results of this test are shown below:

C Product Oil austic Run Conc., TDD" Percent Copper Aged Strip Color These data show that when using an excess amount of sweetening agent the copper strip number of the product oil can be brought to a satisfactory level by using concentrated aqueous caustic solution and treating at elevated temperature.

Test5 1n this test feed A was used. A group of runs were made with and without the use of sweetening agent and also at derent caustic treating temperatures. In each run the liquid SO2 contacting steps were carried out at 4 F. and with a volume ratio of liquid SO2 to feed to the particular contacting step of 0.5. In the multiple step runs the raiiinate and extract phases were separated in the one step and only the ranate phase was charged to the succeeding step. The ranate phases were charged to the aqueous caustic treating step after weathering off substantially all of the occluded and dissolved SO2; the weathered oil had only a very slight SO2 odor. In general the experimental procedure followed that given in the tests above. 1n each run a 10% aqueous NaOH solution was used. The results of these runs are given below:

Product Oil Caustic Run S01 m Treating Mel- Steps Moi Mer-captan Tgrp., captan Coppel. Aged l Num- Strip Color ber I These runs show that a sweet oil cannot be obtained by even three batch extractions with liquid SO2 in the absence of sweetening agent. Runs 19 and 20 show that even though a sweet oil is obtained in a one-stage treatment with liquid SO2 in the presence of sulfuryl chloride, the aged color and copper strip number is unsatisfactory even when caustic treating at elevated temperatures.

Test6 These runs were carried out on the feed and under the conditions of Test 5 and were made for the purpose of noting the effect of caustic treating temperature on the properties of the product oil.

These runs show the adverse effect of the higher boiling components of feed A as against the previously set n out similar runs on feed B.

Test 7 Run 23 was carried out to determine the effect of reversing the order of liquid SO2 contacting on product oil properties. In this run feed A was contacted at 4 F. with liquid SO2 alone, using a 0.5 volume ratio of liquid SO2 to oil, in two batch stages. The rainate phase from the second batch stage was then contacted with liquid SO2 in the same 0.5 ratio and with 1.65 mols of suluryl chloride per mol of mercaptan in the second rafnate phase. The third raffinate phase was treated with 10% aqueous NaOH solution at 77 F. Although the product oil was sweet to the doctor test, the oil had a negative Saybolt color and a black copper strip.

Thus having described the invention, what is claimed is:

l. A process for reiining a sour virgin petroleum distillate boiling in the heavier-than-gasoline range, which process comprises contacting said distillate in the liquid phase in a iirst zone with at least enough liquid SO2 to form separate raffinate and extract phases, in the presence of an amount of a sweetening agent sufficient to substantially sweeten said distillate, which agent is chloride and thionyl chloride, at a temperature below about +70" F. for a time sutlicient to substantially sweeten said distillate, contacting said raiilnate phase in the liquid phase in a second zone, at a temperature below about +70" F., with liquid SO2, in an amount at least suiiicient to form an extract phase and a second rainate phase, and removing SO2 from said second raffinate phase to obtain a substantially sweet product oil.

2. The process of claim l wherein said agent is sulfuryl chloride and the amount present is between about 0.9 and 1.1 mois per mol of mercaptan in said distillate.

3. T he process of claim l wherein said agent is chlorine and the amount present is between about 0.9 and 1.1 mols perrmol ofmercaptan in said distillate.

4. The process of claim 1 wherein said agent is thionyl chloride and the amount present is between about 1.4 and 1.6 inols per mol oi mercaptan in said distillate.

5. The process ot claim 1 wherein said second ratiinate phase is treated with aqueous caustic to remove residual SO2.

6. The process of claim wherein said treating is carried out at a temperature between about 120 and 220 F.

7. The process or" claim 1 wherein the liquid S072 usage in each zone is between about and 500 volume percent, based on the charge oil to each Zone. Y

8. The process of claim l wherein the temperature of contacting in each zone is between about and 70 F.

9. A process for refining a high-sulfur, sour virgin heater oil, which process comprises (l) contacting in the liquid phase said oil, at a temperature between about +30 and 40 F. for a time sutlicient to substantially sweeten said oil, with between about 20 and 80 volume percent of liquid SO2, based on said oil, in the presence of at least about l mol of sulfuryl chloride per mol of mercaptan in said oil, under conditions to form separate raffinate and extract phases, (2) contacting in the liquid phase said rai'linate phase with between about 20 and 80 volumes of liquid SO2 at a temperature between about +30 and 40 F., (3) separating a second raffinate phase from a second extract phase, (4) stripping SO2 from the ratnate of step (3), (5) treating said second raiiinate phase with aqueous caustic solution containing between about 5 and 50 weight percent of alkali-metal hydroxide at a temperaturebetween about and 220 F., in an amount sulicient to neutralize said second raffinate phase and to form a separate aqueous phase and (6) separating a substantially sweet product oil of good aged color and satisfactory copper strip number from said aqueous phase.

` l0. The process of claim 9 wherein the raffinate phase from stepV (3) is contacted in the liquid phase with between about 20 and 80 volumes of liquid SO2 at a tem- 12 perature between about -|-30 and 40 F., another raiiinate phase separated from an extract phase and this raiinate phase is processed in accordance with the following steps of claim 9.

ll. Therprocess of claim 9 wherein the contacting time in said step (l) is between about 2 and 10 minutes.

12. A process for rening a high-sulfur, sour virgin heater oil boiling between about 350 and 625 F., which process comprises (1) contacting said oil with about 50 volume percent, based on said oil, of liquid SO2 in the presence of about 1.3 mois of sulfuryl chloride per inol of rnercaptans in said oil, for about 5 minutes at a temperature of about 0 F., (2) separating an extract phase from a raiiinate phase, (3) contacting said raiiinate phase with about 50 volume 'percent of liquid SO2', based on said rarinate phase, at a temperature of about 0 .F. for about 5 minutes, (4l separating a second extract phase from a second raffinate phase, (5) contacting said second rafnate phase with about 50 volume percent of liquid SO2,v

based on said second raflinate phase, at a temperature of about 0 F. for about 5 minutes, (6) separating a third ratiinate phase from a third extract phase, (7) stripping substantially all of the SO2 from the raliinate phase of step 6), (8) treating the stripped rainate phase with about 50 volume percent of aqueous caustic containing about 25 weight percent of NaOH, at a temperature Vof about F., (9) separating a neutralized oil from an aqueous phase, (l0) washing said oil from step (9) with about 50 volume percent of water and (ll) separating a sweet product oil of satisfactory aged color and copper strip number from an aqueous phase.

13. A process for refining a straight run petroleum distillate boiling in the heavier-than-gasoline range which contains objectionable amounts of mercaptans, which process comprises countercurrently contacting said distillate in the liquid phase with between about 20 and 80 volume percent of liquid SO2 based on said distillate,

introducing into the contacting zone at a point about intermediate between the points of introduction of said distillate and said liquid SO2 an amount of a sweetening agent sulicient to substantially sweeten said distillate,

References Cited inthe rile of this patent UNITED STATES .PATENTS 1,941,25 l Y i Davis Dec. 26, 1933 g FOREIGN PATENTS 298,484

Great Britain Feb. 10, 1930 

13. A PROCESS FOR REFINING A STRAIGHT RUN PETROLEUM DISTILLATE BOILING IN THE HEAVIER-THAN-GASOLINE RANGE WHICH CONTAINS OBJECTIONABLE AMOUNTS OF MERCAPTANS, WHICH PROCESS COMPRISES COUNTERCURRENTLY CONTACTING SAID DISTILLATE IN THE LIQUID PHASE WITH BETWEEN ABOUT 20 AND 80 VOLUME PERCENT OF LIQUID SO2 BASED ON SAID DISTILLATE, INTRODUCING INTO THE CONTACTING ZONE AT A POINT ABOUT INTERMEDIATE BETWEEN THE POINTS OF INTRODUCTION OF SAID DISTILLATE AND SAID LIQUID SO2 AN AMOUNT OF A SWEETENING AGENT SUFFICIENT TO SUBSTANTIALLY SWEETEN AND DISTILLATE, WHICH AGENT IS SELECTED FROM THE GROUP CONSISTING OF CHLORINE, SULFURYL CHLORIDE AND THIONYL CHLORIDE AT A TEMPERATURE BETWEEN ABOUT +30* AND -40* F. FOR A TIME SUFFICIENT TO SUBSTANTIALLY SWEETEN SAID DISTILLATE, SEPARATING A RAFFINATE PHASE FROM AN EXTRACT PHASE AND RECOVERING FROM SAID RAFFINATE PHASE A SUBSTANTIALLY SWEET, SO2-FREE PRODUCT OIL. 